Uranus
Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (mythology), Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars (mythology), Mars), grandfather ...
, the seventh planet of the
Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
, has 27 known
moons
A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body (or sometimes another natural satellite). Natural satellites are often colloquially referred to as ''moons'' ...
, most of which are named after characters that appear in, or are mentioned in, the works of
William Shakespeare
William Shakespeare ( 26 April 1564 – 23 April 1616) was an English playwright, poet and actor. He is widely regarded as the greatest writer in the English language and the world's pre-eminent dramatist. He is often called England's nation ...
and
Alexander Pope
Alexander Pope (21 May 1688 O.S. – 30 May 1744) was an English poet, translator, and satirist of the Enlightenment era who is considered one of the most prominent English poets of the early 18th century. An exponent of Augustan literature, ...
. Uranus's moons are divided into three groups: thirteen inner moons, five
major moon
A planetary-mass moon is a planetary-mass object that is also a natural satellite. They are large and ellipsoidal (sometimes spherical) in shape. Two moons in the Solar System are larger than the planet Mercury (though less massive): Ganymede a ...
s, and nine irregular moons. The inner and major moons all have prograde orbits, while orbits of the irregulars are mostly retrograde. The inner moons are small dark bodies that share common properties and origins with Uranus's rings. The five major moons are ellipsoidal, indicating that they reached
hydrostatic equilibrium
In fluid mechanics, hydrostatic equilibrium (hydrostatic balance, hydrostasy) is the condition of a fluid or plastic solid at rest, which occurs when external forces, such as gravity, are balanced by a pressure-gradient force. In the planetary ...
at some point in their past (and may still be in equilibrium), and four of them show signs of internally driven processes such as canyon formation and volcanism on their surfaces. The largest of these five, Titania, is 1,578 km in diameter and the eighth-largest moon in the Solar System, about one-twentieth the mass of the Earth's
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
. The orbits of the regular moons are nearly
coplanar
In geometry, a set of points in space are coplanar if there exists a geometric plane that contains them all. For example, three points are always coplanar, and if the points are distinct and non-collinear, the plane they determine is unique. Howe ...
with Uranus's equator, which is tilted 97.77° to its orbit. Uranus's irregular moons have elliptical and strongly inclined (mostly retrograde) orbits at large distances from the planet.
William Herschel
Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline H ...
Oberon
Oberon () is a king of the fairies in medieval and Renaissance literature. He is best known as a character in William Shakespeare's play ''A Midsummer Night's Dream'', in which he is King of the Fairies and spouse of Titania, Queen of the Fair ...
, in 1787. The other three ellipsoidal moons were discovered in 1851 by
William Lassell
William Lassell (18 June 1799 – 5 October 1880) was an English merchant and astronomer.Ariel
Ariel may refer to:
Film and television
*Ariel Award, a Mexican Academy of Film award
* ''Ariel'' (film), a 1988 Finnish film by Aki Kaurismäki
* ''ARIEL Visual'' and ''ARIEL Deluxe'', 1989 and 1991 anime video series based on the novel series ...
Gerard Kuiper
Gerard Peter Kuiper (; ; born Gerrit Pieter Kuiper; 7 December 1905 – 23 December 1973) was a Dutch astronomer, planetary scientist, selenographer, author and professor. He is the eponymous namesake of the Kuiper belt.
Kuiper is ...
hydrostatic equilibrium
In fluid mechanics, hydrostatic equilibrium (hydrostatic balance, hydrostasy) is the condition of a fluid or plastic solid at rest, which occurs when external forces, such as gravity, are balanced by a pressure-gradient force. In the planetary ...
, and so would be considered dwarf planets if they were in direct orbit about the Sun. The remaining moons were discovered after 1985, either during the ''
Voyager 2
''Voyager 2'' is a space probe launched by NASA on August 20, 1977, to study the outer planets and interstellar space beyond the Sun's heliosphere. As a part of the Voyager program, it was launched 16 days before its twin, ''Voyager 1'', on ...
'' flyby mission or with the aid of advanced
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
-based telescopes.
Discovery
The first two moons to be discovered were Titania and
Oberon
Oberon () is a king of the fairies in medieval and Renaissance literature. He is best known as a character in William Shakespeare's play ''A Midsummer Night's Dream'', in which he is King of the Fairies and spouse of Titania, Queen of the Fair ...
, which were spotted by
Sir William Herschel
Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline H ...
on January 11, 1787, six years after he had discovered the planet itself. Later, Herschel thought he had discovered up to six moons (see below) and perhaps even a ring. For nearly 50 years, Herschel's instrument was the only one with which the moons had been seen. In the 1840s, better instruments and a more favorable position of Uranus in the sky led to sporadic indications of satellites additional to Titania and Oberon. Eventually, the next two moons,
Ariel
Ariel may refer to:
Film and television
*Ariel Award, a Mexican Academy of Film award
* ''Ariel'' (film), a 1988 Finnish film by Aki Kaurismäki
* ''ARIEL Visual'' and ''ARIEL Deluxe'', 1989 and 1991 anime video series based on the novel series ...
William Lassell
William Lassell (18 June 1799 – 5 October 1880) was an English merchant and astronomer. The Roman numbering scheme of Uranus's moons was in a state of flux for a considerable time, and publications hesitated between Herschel's designations (where Titania and Oberon are Uranus II and IV) and William Lassell's (where they are sometimes I and II). With the confirmation of Ariel and Umbriel, Lassell numbered the moons I through IV from Uranus outward, and this finally stuck. In 1852, Herschel's son
John Herschel
Sir John Frederick William Herschel, 1st Baronet (; 7 March 1792 – 11 May 1871) was an English polymath active as a mathematician, astronomer, chemist, inventor, experimental photographer who invented the blueprint and did botanical wor ...
gave the four then-known moons their names.
No other discoveries were made for almost another century. In 1948,
Gerard Kuiper
Gerard Peter Kuiper (; ; born Gerrit Pieter Kuiper; 7 December 1905 – 23 December 1973) was a Dutch astronomer, planetary scientist, selenographer, author and professor. He is the eponymous namesake of the Kuiper belt.
Kuiper is ...
at the
McDonald Observatory
McDonald Observatory is an astronomical observatory located near unincorporated community of Fort Davis in Jeff Davis County, Texas, United States. The facility is located on Mount Locke in the Davis Mountains of West Texas, with additional facil ...
discovered the smallest and the last of the five large, spherical moons, Miranda. Decades later, the flyby of the ''
Voyager 2
''Voyager 2'' is a space probe launched by NASA on August 20, 1977, to study the outer planets and interstellar space beyond the Sun's heliosphere. As a part of the Voyager program, it was launched 16 days before its twin, ''Voyager 1'', on a ...
'' space probe in January 1986 led to the discovery of ten further inner moons. Another satellite, Perdita, was discovered in 1999 after studying old ''Voyager'' photographs.
Uranus was the last giant planet without any known
irregular moon
In astronomy, an irregular moon, irregular satellite or irregular natural satellite is a natural satellite following a distant, inclined, and often eccentric and retrograde orbit. They have been captured by their parent planet, unlike regular sat ...
s, but since 1997 nine distant irregular moons have been identified using ground-based telescopes. Two more small inner moons,
Cupid
In classical mythology, Cupid (Latin Cupīdō , meaning "passionate desire") is the god of desire, lust, erotic love, attraction and affection. He is often portrayed as the son of the love goddess Venus (mythology), Venus and the god of war Mar ...
Hubble Space Telescope
The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...
in 2003. As of 2020, the moon
Margaret
Margaret is a female first name, derived via French () and Latin () from grc, μαργαρίτης () meaning "pearl". The Greek is borrowed from Persian.
Margaret has been an English name since the 11th century, and remained popular througho ...
was the last Uranian moon discovered, and its characteristics were published in October 2003.
Oberon
Oberon () is a king of the fairies in medieval and Renaissance literature. He is best known as a character in William Shakespeare's play ''A Midsummer Night's Dream'', in which he is King of the Fairies and spouse of Titania, Queen of the Fair ...
on January 11, 1787, he subsequently believed that he had observed four other moons: two on January 18 and February 9, 1790, and two more on February 28 and March 26, 1794. It was thus believed for many decades thereafter that Uranus had a system of six satellites, though the four latter moons were never confirmed by any other astronomer. Lassell's observations of 1851, in which he discovered
Ariel
Ariel may refer to:
Film and television
*Ariel Award, a Mexican Academy of Film award
* ''Ariel'' (film), a 1988 Finnish film by Aki Kaurismäki
* ''ARIEL Visual'' and ''ARIEL Deluxe'', 1989 and 1991 anime video series based on the novel series ...
and Umbriel, however, failed to support Herschel's observations; Ariel and Umbriel, which Herschel certainly ought to have seen if he had seen any satellites beside Titania and Oberon, did not correspond to any of Herschel's four additional satellites in orbital characteristics. Herschel's four spurious satellites were thought to have
sidereal period
The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets, ...
s of 5.89 days (interior to Titania), 10.96 days (between Titania and Oberon), 38.08 days, and 107.69 days (exterior to Oberon). It was therefore concluded that Herschel's four satellites were spurious, probably arising from the misidentification of faint stars in the vicinity of Uranus as satellites, and the credit for the discovery of Ariel and Umbriel was given to Lassell.
Names
Although the first two Uranian moons were discovered in 1787, they were not named until 1852, a year after two more moons had been discovered. The responsibility for naming was taken by
John Herschel
Sir John Frederick William Herschel, 1st Baronet (; 7 March 1792 – 11 May 1871) was an English polymath active as a mathematician, astronomer, chemist, inventor, experimental photographer who invented the blueprint and did botanical wor ...
, son of the discoverer of Uranus. Herschel, instead of assigning names from
Greek mythology
A major branch of classical mythology, Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the Cosmogony, origin and Cosmology#Metaphysical co ...
, named the moons after magical spirits in
English literature
English literature is literature written in the English language from United Kingdom, its crown dependencies, the Republic of Ireland, the United States, and the countries of the former British Empire. ''The Encyclopaedia Britannica'' defines E ...
: the fairies Oberon and Titania from
William Shakespeare
William Shakespeare ( 26 April 1564 – 23 April 1616) was an English playwright, poet and actor. He is widely regarded as the greatest writer in the English language and the world's pre-eminent dramatist. He is often called England's nation ...
's ''
A Midsummer Night's Dream
''A Midsummer Night's Dream'' is a comedy written by William Shakespeare 1595 or 1596. The play is set in Athens, and consists of several subplots that revolve around the marriage of Theseus and Hippolyta. One subplot involves a conflict amon ...
'', and the
sylph
A sylph (also called sylphid) is an air spirit stemming from the 16th-century works of Paracelsus, who describes sylphs as (invisible) beings of the air, his elementals of air. A significant number of subsequent literary and occult works have be ...
Ariel and
gnome
A gnome is a mythological creature and diminutive spirit in Renaissance magic and alchemy, first introduced by Paracelsus in the 16th century and later adopted by more recent authors including those of modern fantasy literature. Its characte ...
Umbriel from
Alexander Pope
Alexander Pope (21 May 1688 O.S. – 30 May 1744) was an English poet, translator, and satirist of the Enlightenment era who is considered one of the most prominent English poets of the early 18th century. An exponent of Augustan literature, ...
's ''
The Rape of the Lock
''The Rape of the Lock'' is a mock-heroic narrative poem written by Alexander Pope. One of the most commonly cited examples of high burlesque, it was first published anonymously in Lintot's ''Miscellaneous Poems and Translations'' (May 1712) ...
'' (Ariel is also a sprite in Shakespeare's '' The Tempest''). The reasoning was presumably that Uranus, as god of the sky and air, would be attended by spirits of the air.
Subsequent names, rather than continuing the airy spirits theme (only Puck and Mab continued the trend), have focused on Herschel's source material. In 1949, the fifth moon, Miranda, was named by its discoverer
Gerard Kuiper
Gerard Peter Kuiper (; ; born Gerrit Pieter Kuiper; 7 December 1905 – 23 December 1973) was a Dutch astronomer, planetary scientist, selenographer, author and professor. He is the eponymous namesake of the Kuiper belt.
Kuiper is ...
after a thoroughly mortal character in Shakespeare's '' The Tempest''. The current
IAU
The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach ...
practice is to name moons after characters from Shakespeare's plays and ''The Rape of the Lock'' (although at present only Ariel, Umbriel, and Belinda have names drawn from the latter; all the rest are from Shakespeare). The outer retrograde moons are all named after characters from one play, ''The Tempest''; the sole known outer prograde moon,
Margaret
Margaret is a female first name, derived via French () and Latin () from grc, μαργαρίτης () meaning "pearl". The Greek is borrowed from Persian.
Margaret has been an English name since the 11th century, and remained popular througho ...
, is named from ''
Much Ado About Nothing
''Much Ado About Nothing'' is a comedy by William Shakespeare thought to have been written in 1598 and 1599.See textual notes to ''Much Ado About Nothing'' in ''The Norton Shakespeare'' ( W. W. Norton & Company, 1997 ) p. 1387 The play ...
''.
* ''
The Rape of the Lock
''The Rape of the Lock'' is a mock-heroic narrative poem written by Alexander Pope. One of the most commonly cited examples of high burlesque, it was first published anonymously in Lintot's ''Miscellaneous Poems and Translations'' (May 1712) ...
'' (a poem by
Alexander Pope
Alexander Pope (21 May 1688 O.S. – 30 May 1744) was an English poet, translator, and satirist of the Enlightenment era who is considered one of the most prominent English poets of the early 18th century. An exponent of Augustan literature, ...
):
** Ariel, Umbriel, Belinda
* Plays by
William Shakespeare
William Shakespeare ( 26 April 1564 – 23 April 1616) was an English playwright, poet and actor. He is widely regarded as the greatest writer in the English language and the world's pre-eminent dramatist. He is often called England's nation ...
:
** ''
A Midsummer Night's Dream
''A Midsummer Night's Dream'' is a comedy written by William Shakespeare 1595 or 1596. The play is set in Athens, and consists of several subplots that revolve around the marriage of Theseus and Hippolyta. One subplot involves a conflict amon ...
'': Titania, Oberon, Puck
** '' The Tempest'': (Ariel), Miranda, Caliban, Sycorax, Prospero, Setebos, Stephano, Trinculo, Francisco, Ferdinand
** ''
King Lear
''King Lear'' is a tragedy written by William Shakespeare.
It is based on the mythological Leir of Britain. King Lear, in preparation for his old age, divides his power and land between two of his daughters. He becomes destitute and insane an ...
'': Cordelia
** ''
Hamlet
''The Tragedy of Hamlet, Prince of Denmark'', often shortened to ''Hamlet'' (), is a tragedy written by William Shakespeare sometime between 1599 and 1601. It is Shakespeare's longest play, with 29,551 words. Set in Denmark, the play depicts ...
'': Ophelia
** ''
The Taming of the Shrew
''The Taming of the Shrew'' is a comedy by William Shakespeare, believed to have been written between 1590 and 1592. The play begins with a framing device, often referred to as the induction, in which a mischievous nobleman tricks a drunken ...
'': Bianca
** ''
Troilus and Cressida
''Troilus and Cressida'' ( or ) is a play by William Shakespeare, probably written in 1602.
At Troy during the Trojan War, Troilus and Cressida begin a love affair. Cressida is forced to leave Troy to join her father in the Greek camp. Meanwh ...
'': Cressida
** ''
Othello
''Othello'' (full title: ''The Tragedy of Othello, the Moor of Venice'') is a tragedy written by William Shakespeare, probably in 1603, set in the contemporary Ottoman–Venetian War (1570–1573) fought for the control of the Island of Cypru ...
'': Desdemona
** ''
Romeo and Juliet
''Romeo and Juliet'' is a Shakespearean tragedy, tragedy written by William Shakespeare early in his career about the romance between two Italian youths from feuding families. It was among Shakespeare's most popular plays during his lifetim ...
'': Juliet, Mab
** ''
The Merchant of Venice
''The Merchant of Venice'' is a play by William Shakespeare, believed to have been written between 1596 and 1598. A merchant in Venice named Antonio defaults on a large loan provided by a Jewish moneylender, Shylock.
Although classified as ...
'': Portia
** ''
As You Like It
''As You Like It'' is a pastoral comedy by William Shakespeare believed to have been written in 1599 and first published in the First Folio in 1623. The play's first performance is uncertain, though a performance at Wilton House in 1603 has b ...
'': Rosalind
** ''
Much Ado About Nothing
''Much Ado About Nothing'' is a comedy by William Shakespeare thought to have been written in 1598 and 1599.See textual notes to ''Much Ado About Nothing'' in ''The Norton Shakespeare'' ( W. W. Norton & Company, 1997 ) p. 1387 The play ...
'': Margaret
** ''
The Winter's Tale
''The Winter's Tale'' is a play by William Shakespeare originally published in the First Folio of 1623. Although it was grouped among the comedies, many modern editors have relabelled the play as one of Shakespeare's late romances. Some criti ...
'': Perdita
** ''
Timon of Athens
''Timon of Athens'' (''The Life of Tymon of Athens'') is a play written by William Shakespeare and probably also Thomas Middleton in about 1606. It was published in the ''First Folio'' in 1623. Timon lavishes his wealth on parasitic companion ...
'': Cupid
Some
asteroid
An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere.
...
s, also named after the same Shakespearean characters, share names with moons of Uranus:
171 Ophelia
Ophelia (minor planet designation: 171 Ophelia) is a large, dark Themistian asteroid that was discovered by French astronomer Alphonse Borrelly on 13 January 1877, and named after Ophelia in Shakespeare's ''Hamlet''.
This asteroid is a member of ...
,
218 Bianca
Bianca ( minor planet designation: 218 Bianca) is a sizeable Main belt asteroid. It is an S-type asteroid. It was discovered by Johann Palisa on 4 September 1880, in Pola and was named after the Austro-Hungarian opera singer Bianca Bianchi ( ...
,
593 Titania
Titania ( minor planet designation: 593 Titania) is a minor planet orbiting the Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in ...
,
666 Desdemona
666 Desdemona is a stony asteroid from the middle region of the asteroid belt, approximately 29 kilometers in diameter. It was discovered on 23 July 1908, by German astronomer August Kopff at Heidelberg Observatory in southern Germany, and named ...
,
763 Cupido
763 Cupido ('' prov. designation:'' ''or'' ) is a Flora asteroid, tumbler and slow rotator from the inner regions of the asteroid belt, approximately in diameter. It was discovered on 25 September 1913, by German astronomer Franz Kaiser at t ...
The Uranian satellite system is the least massive among those of the
giant planet
The giant planets constitute a diverse type of planet much larger than Earth. They are usually primarily composed of low-boiling-point materials (volatiles), rather than rock or other solid matter, but massive solid planets can also exist. Ther ...
s. Indeed, the combined mass of the five major satellites is less than half that of
Triton
Triton commonly refers to:
* Triton (mythology), a Greek god
* Triton (moon), a satellite of Neptune
Triton may also refer to:
Biology
* Triton cockatoo, a parrot
* Triton (gastropod), a group of sea snails
* ''Triton'', a synonym of ''Triturus' ...
(the seventh-largest moon in the Solar System) alone. The largest of the satellites, Titania, has a radius of 788.9 km, or less than half that of the
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
, but slightly more than that of Rhea, the second-largest moon of
Saturn
Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
. Uranus is about 10,000 times more massive than its moons.
Inner moons
As of 2020, Uranus is known to have 13 inner moons. Their orbits lie inside that of Miranda. All inner moons are intimately connected with the
rings of Uranus
The rings of Uranus are intermediate in complexity between the more extensive set around Saturn and the simpler systems around Jupiter and Neptune. The rings of Uranus were discovered on March 10, 1977, by James L. Elliot, Edward W. Dunham, and J ...
, which probably resulted from the fragmentation of one or several small inner moons. The two innermost moons (
Cordelia
Cordelia is a feminine given name. It was borne by the tragic heroine of Shakespeare's ''King Lear'' (1606), a character based on the List of legendary kings of Britain, legendary queen Cordelia of Britain, Cordelia. The name is of uncertain origi ...
and
Ophelia
Ophelia () is a character in William Shakespeare's drama ''Hamlet'' (1599–1601). She is a young noblewoman of Denmark, the daughter of Polonius, sister of Laertes and potential wife of Prince Hamlet, who, due to Hamlet's actions, ends up in ...
) are
shepherds
A shepherd or sheepherder is a person who tends, herds, feeds, or guards flocks of sheep. ''Shepherd'' derives from Old English ''sceaphierde (''sceap'' 'sheep' + ''hierde'' 'herder'). ''Shepherding is one of the world's oldest occupations, i ...
of Uranus's ε ring, whereas the small moon Mab is a source of Uranus's outermost μ ring. There may be two additional small (2–7 km in radius) undiscovered shepherd moons located about 100 km exterior to Uranus's α and β rings.
At 162 km, Puck is the largest of the inner moons of Uranus and the only one imaged by ''Voyager 2'' in any detail. Puck and Mab are the two outermost inner satellites of Uranus. All inner moons are dark objects; their geometrical
albedo
Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...
is less than 10%. They are composed of water ice contaminated with a dark material, probably radiation-processed organics.
The small inner moons constantly
perturb
Perturbation or perturb may refer to:
* Perturbation theory, mathematical methods that give approximate solutions to problems that cannot be solved exactly
* Perturbation (geology), changes in the nature of alluvial deposits over time
* Perturbatio ...
each other. The system is
chaotic
Chaotic was originally a Danish trading card game. It expanded to an online game in America which then became a television program based on the game. The program was able to be seen on 4Kids TV (Fox affiliates, nationwide), Jetix, The CW4Kid ...
and apparently unstable. Simulations show that the moons may perturb each other into crossing orbits, which may eventually result in collisions between the moons.
Desdemona
Desdemona () is a character in William Shakespeare's play ''Othello'' (c. 1601–1604). Shakespeare's Desdemona is a Venetian beauty who enrages and disappoints her father, a Venetian senator, when she elopes with Othello, a Moorish Venetian ...
may collide with either
Cressida
Cressida (; also Criseida, Cresseid or Criseyde) is a character who appears in many Medieval and Renaissance retellings of the story of the Trojan War. She is a Trojan woman, the daughter of Calchas, a Greek seer. She falls in love with Troilus, ...
or
Juliet
Juliet Capulet () is the female protagonist in William Shakespeare's romantic tragedy ''Romeo and Juliet''. A 13-year-old girl, Juliet is the only daughter of the patriarch of the House of Capulet. She falls in love with the male protagonist R ...
within the next 100 million years.
Large moons
Uranus has five
major moon
A planetary-mass moon is a planetary-mass object that is also a natural satellite. They are large and ellipsoidal (sometimes spherical) in shape. Two moons in the Solar System are larger than the planet Mercury (though less massive): Ganymede a ...
Ariel
Ariel may refer to:
Film and television
*Ariel Award, a Mexican Academy of Film award
* ''Ariel'' (film), a 1988 Finnish film by Aki Kaurismäki
* ''ARIEL Visual'' and ''ARIEL Deluxe'', 1989 and 1991 anime video series based on the novel series ...
Oberon
Oberon () is a king of the fairies in medieval and Renaissance literature. He is best known as a character in William Shakespeare's play ''A Midsummer Night's Dream'', in which he is King of the Fairies and spouse of Titania, Queen of the Fair ...
. They range in diameter from 472 km for Miranda to 1578 km for Titania. All these moons are relatively dark objects: their geometrical albedo varies between 30 and 50%, whereas their
Bond albedo
The Bond albedo (or ''spheric albedo'' or ''planetary albedo'' or ''bolometric albedo''), named after the American astronomer George Phillips Bond (1825–1865), who originally proposed it, is the fraction of power in the total electromagnetic rad ...
is between 10 and 23%. Umbriel is the darkest moon and Ariel the brightest. The masses of the moons range from 6.7 kg (Miranda) to 3.5 kg (Titania). For comparison, the
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
has a mass of 7.5 kg. The major moons of Uranus are thought to have formed in the
accretion disc
An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is typically a star. Friction, uneven irradiance, magnetohydrodynamic effects, and other f ...
, which existed around Uranus for some time after its formation or resulted from a large impact suffered by
Uranus
Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (mythology), Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars (mythology), Mars), grandfather ...
early in its history. This view is supported by their large thermal inertia, a surface property they share with
dwarf planet
A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to p ...
s like
Pluto
Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the S ...
and
Haumea
Haumea (minor-planet designation 136108 Haumea) is a dwarf planet located trans-Neptunian object, beyond Neptune's orbit. It was discovered in 2004 by a team headed by Michael E. Brown, Mike Brown of Caltech at the Palomar Observatory in the United ...
. It differs strongly from the thermal behaviour of the Uranian irregular moons that is comparable to classical
trans-Neptunian object
A trans-Neptunian object (TNO), also written transneptunian object, is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune, which has a semi-major axis of 30.1 astronomical units (au).
Typically, ...
s. This suggests a separate origin.
All major moons comprise approximately equal amounts rock and ice, except Miranda, which is made primarily of ice. The ice component may include
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...
and
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
. Their surfaces are heavily cratered, though all of them (except Umbriel) show signs of
endogenic
Endogenous substances and processes are those that originate from within a living system such as an organism, tissue, or cell.
In contrast, exogenous substances and processes are those that originate from outside of an organism.
For example, e ...
resurfacing in the form of lineaments (canyons) and, in the case of Miranda, ovoid race-track like structures called coronae. Extensional processes associated with upwelling
diapir
A diapir (; , ) is a type of igneous intrusion in which a more mobile and ductily deformable material is forced into brittle overlying rocks. Depending on the tectonic environment, diapirs can range from idealized mushroom-shaped Rayleigh–T ...
s are likely responsible for the origin of the coronae. Ariel appears to have the youngest surface with the fewest impact craters, while Umbriel's appears oldest. A past 3:1
orbital resonance
In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relationsh ...
between Miranda and Umbriel and a past 4:1 resonance between Ariel and Titania are thought to be responsible for the heating that caused substantial endogenic activity on Miranda and Ariel.
One piece of evidence for such a past resonance is Miranda's unusually high orbital
inclination
Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object ...
(4.34°) for a body so close to the planet. The largest Uranian moons may be internally differentiated, with rocky cores at their centers surrounded by ice mantles. Titania and Oberon may harbor liquid water oceans at the core/mantle boundary. The major moons of Uranus are airless bodies. For instance, Titania was shown to possess no atmosphere at a pressure larger than 10–20 nanobar.
The path of the Sun in the local sky over the course of a local day during Uranus's and its major moons' summer solstice is quite different from that seen on most other
Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
worlds. The major moons have almost exactly the same rotational axial tilt as Uranus (their axes are parallel to that of Uranus). The Sun would appear to follow a circular path around Uranus's celestial pole in the sky, at the closest about 7 degrees from it, during the hemispheric summer. Near the equator, it would be seen nearly due north or due south (depending on the season). At latitudes higher than 7°, the Sun would trace a circular path about 15 degrees in diameter in the sky, and never set during the hermispheric summer, moving to a position over the celestial equator during the Uranian equinox, and then invisible below the horizon during the hemispheric winter.
Irregular moons
As of 2005 Uranus is known to have nine irregular moons, which orbit it at a distance much greater than that of Oberon, the furthest of the large moons. All the irregular moons are probably captured objects that were trapped by Uranus soon after its formation. The diagram illustrates the orbits of those
irregular moon
In astronomy, an irregular moon, irregular satellite or irregular natural satellite is a natural satellite following a distant, inclined, and often eccentric and retrograde orbit. They have been captured by their parent planet, unlike regular sat ...
s discovered so far. The moons above the X axis are prograde, those beneath are retrograde. The radius of the Uranian
Hill sphere
The Hill sphere of an astronomical body is the region in which it dominates the attraction of satellites. To be retained by a planet, a moon must have an orbit that lies within the planet's Hill sphere. That moon would, in turn, have a Hill sp ...
is approximately 73 million km.
Uranus's irregular moons range in size from 120–200 km (
Sycorax
Sycorax is an unseen character in William Shakespeare's play ''The Tempest'' (1611). She is a vicious and powerful witch and the mother of Caliban (character), Caliban, one of the few native inhabitants of the island on which Prospero, the he ...
) to about 20 km ( Trinculo). Unlike Jupiter's irregulars, Uranus's show no correlation of axis with
inclination
Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object ...
. Instead, the retrograde moons can be divided into two groups based on axis/
orbital eccentricity
In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values betwee ...
. The inner group includes those satellites closer to Uranus (a < 0.15 rH) and moderately eccentric (~0.2), namely
Francisco
Francisco is the Spanish and Portuguese form of the masculine given name ''Franciscus''.
Nicknames
In Spanish, people with the name Francisco are sometimes nicknamed "Paco (name), Paco". Francis of Assisi, San Francisco de Asís was known as '' ...
,
Caliban
Caliban ( ), son of the witch Sycorax, is an important character in William Shakespeare's play '' The Tempest''.
His character is one of the few Shakespearean figures to take on a life of its own "outside" Shakespeare's own work: as Russell ...
, Stephano, and Trinculo. The outer group (a > 0.15 rH) includes satellites with high eccentricity (~0.5): Sycorax,
Prospero
Prospero ( ) is a fictional character and the protagonist of William Shakespeare's play '' The Tempest''.
Prospero is the rightful Duke of Milan, whose usurping brother, Antonio, had put him (with his three-year-old daughter, Miranda) to sea ...
Ferdinand
Ferdinand is a Germanic name composed of the elements "protection", "peace" (PIE "to love, to make peace") or alternatively "journey, travel", Proto-Germanic , abstract noun from root "to fare, travel" (PIE , "to lead, pass over"), and "co ...
.
The intermediate inclinations 60° < i < 140° are devoid of known moons due to the Kozai instability. In this instability region, solar perturbations at apoapse cause the moons to acquire large eccentricities that lead to collisions with inner satellites or ejection. The lifetime of moons in the instability region is from 10 million to a billion years.
Margaret
Margaret is a female first name, derived via French () and Latin () from grc, μαργαρίτης () meaning "pearl". The Greek is borrowed from Persian.
Margaret has been an English name since the 11th century, and remained popular througho ...
is the only known irregular prograde moon of Uranus, and it currently has the most eccentric orbit of any moon in the Solar System, though Neptune's moon
Nereid
In Greek mythology, the Nereids or Nereides ( ; grc, Νηρηΐδες, Nērēḯdes; , also Νημερτές) are sea nymphs (female spirits of sea waters), the 50 daughters of the 'Old Man of the Sea' Nereus and the Oceanids, Oceanid Doris ...
has a higher mean eccentricity. As of 2008, Margaret's eccentricity is 0.7979.
List
The Uranian moons are listed here by orbital period, from shortest to longest. Moons massive enough for their surfaces to have collapsed into a
spheroid
A spheroid, also known as an ellipsoid of revolution or rotational ellipsoid, is a quadric surface obtained by rotating an ellipse about one of its principal axes; in other words, an ellipsoid with two equal semi-diameters. A spheroid has cir ...
are highlighted in light blue and bolded. The inner and major moons all have prograde orbits. Irregular moons with retrograde orbits are shown in dark grey. Margaret, the only known irregular moon of Uranus with a prograde orbit, is shown in light grey. The orbits and mean distances of the irregular moons are variable over short timescales due to frequent planetary and solar perturbations, therefore the listed orbital elements of all irregular moons are averaged over a 8,000-year
numerical integration
In analysis, numerical integration comprises a broad family of algorithms for calculating the numerical value of a definite integral, and by extension, the term is also sometimes used to describe the numerical solution of differential equations ...
by Brozović and Jacobson (2009). Their orbital elements are all based on the
epoch
In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured.
The moment of epoch is usually decided by ...
of 1 January 2000
Terrestrial Time
Terrestrial Time (TT) is a modern astronomical time standard defined by the International Astronomical Union, primarily for time-measurements of astronomical observations made from the surface of Earth.
For example, the Astronomical Almanac uses T ...
.
''Sources:'' NASA/NSSDC, Sheppard, et al. 2005. For the recently discovered outer irregular moons (Francisco through Ferdinand) the most accurate orbital data can be generated with the
Minor Planet Center
The Minor Planet Center (MPC) is the official body for observing and reporting on minor planets under the auspices of the International Astronomical Union (IAU). Founded in 1947, it operates at the Smithsonian Astrophysical Observatory.
Function
...
's Natural Satellites Ephemeris Service. The irregulars are significantly perturbed by the Sun.
See also
*
List of natural satellites
The Solar System's planets, and its most likely dwarf planets, are known to be orbited by at least 221 natural satellites, or moons. At least 20 of them are large enough to be gravitationally rounded; of these, all are covered by a crust of ...
Notes
References
External links
*
Scott S. Sheppard
Scott Sander Sheppard (born 1977) is an American astronomer and a discoverer of numerous moons, comets and minor planets in the outer Solar System.
He is an astronomer in the Department of Terrestrial Magnetism at the Carnegie Institution for Scie ...